1. Field of the Invention
The present invention relates to internal combustion engines having direct acting camshaft and tappet arrangements.
2. Discussion of Prior Art
Poppet valve drive arrangements for internal combustion engines typically utilize either hydraulic lash adjusters or manually adjustable tappets or rockers. In the event that hydraulic lash adjusters are not employed, it is necessary to periodically re-measure the lash and provide necessary shims and/or other adjustments in order to permit necessary clearance between the cam lobe on its base circle and the accompanying valve tappet.
With overhead camshaft engines equipped with direct acting mechanical bucket tappets, it is necessary to measure the lash and then provide the required shims. This is often done by removing shims, in which case it is necessary with many engines to physically displace the camshaft to allow access to the tappets. With four-valve cylinder heads, access to the tappets is typically very limited and requires considerable displacement of the camshaft. This, in turn, may create problems if, for example, a camshaft drive chain or belt tensioner automatically rachets to take up slack in the chain drive or belt mechanism. It is understood that tilting of the camshaft may result in temporary displacement of the camshaft drive sprocket in a direction introducing slack in the drive chain or belt.
If tilting of camshaft results in taking up play by an automatically racheting tensioner, catastrophic results may ensue if the engine is not freewheeling, i.e., if the engine's pistons are not clearanced to remain free of the valves should the valves be open when the piston is at top dead center, as during the overlap period between the exhaust and intake strokes. And, even where a tensioner maladjustment is discovered prior to placing the engine back in service, a time-consuming repair will be necessitated because removal of the engine's front cover will, in all likelihood, be needed.
It is known to tilt the camshaft to allow access to mechanical tappets or buckets so as to allow adjustment of the tappets, and this process is typically done by wedging an object under the camshaft. A problem with this practice is that while merely wedging an object under the camshaft, it is difficult to determine how far the camshaft may be lifted without causing a problem with a chain or belt tensioner, as described above.
A system and method according to the present invention provides a reliable and repeatable method and means for lifting and tilting a camshaft sufficiently to allow access to the underlying tappets, without engendering risk that the camshaft drive tensioner will erroneously actuate and without risking damage to the camshaft.